Heretofore, the internal porosity of fine particles has been determined by mercury intrusion porosimetry, a procedure by which mercury is forced under increasing pressure through a graduated penetrometer into the open pores of a particle sample. The volume of mercury forced into the pores is determined and the interior pore volume can be determined from that measurement. However, this method (ASTM D2873-70) is time-consuming and requires elaborate equipment.
The present invention presents a method of determining internal porosity by measuring forces on an obstacle suspended in a bed containing said powder. The stress distributions in a loosely packed bed of powder have been analyzed, for example, by R. M. Nedderman in "The Theoretical Prediction of Stress Distribution in Hoppers," Tran. I. Chem. Eng., 60,259 (1982), and by Atkinson, et al. in "The Forces on Obstacles Suspended in Flowing Granular Materials," Chem. Eng. Sci. 38, 91 (1983). Nedderman and Atkinson et al. both studied the axial forces applied to an object suspended in a powder medium as the powder flowed by gravity through a funnel outlet out of the powder bed. Other work includes the study of Kaye, et al, on "The Effect of Vibration on the Rheology of Powders", published in a paper presented at a conference entitled "International Powder and Bulk Solids Handling and Processing," held in Atlanta, Ga., May 24-26, 1983, and also an oral presentation of W. K. Lee presented at the 1982 AIChe Annual Meeting held Nov. 14-19, 1982 in Los Angeles, Calif., and at the 57th Annual Meeting of the Society of Rheology Oct. 14-17, 1985 in Ann Arbor, Mich. Kaye et al. recorded the change in the force necessary to draw sandpaper out of a powder bed as the bed is subjected to vibration. Lee studied the force necessary to draw a plate from a loosely packed powder bed as a function of the depth of insertion of the plate.